blob: 077b635c8b0d4eba1abe656300131357ea6050d8 [file] [log] [blame]
/* vi: set sw=4 ts=4: */
* Mini umount implementation for busybox
* Copyright (C) 1999-2004 by Erik Andersen <>
* Copyright (C) 2005 by Rob Landley <>
* Licensed under GPLv2, see file LICENSE in this source tree.
//config:config UMOUNT
//config: bool "umount (5.1 kb)"
//config: default y
//config: select PLATFORM_LINUX
//config: help
//config: When you want to remove a mounted filesystem from its current mount
//config: point, for example when you are shutting down the system, the
//config: 'umount' utility is the tool to use. If you enabled the 'mount'
//config: utility, you almost certainly also want to enable 'umount'.
//config:config FEATURE_UMOUNT_ALL
//config: bool "Support -a (unmount all)"
//config: default y
//config: depends on UMOUNT
//config: help
//config: Support -a option to unmount all currently mounted filesystems.
//applet:IF_UMOUNT(APPLET_NOEXEC(umount, umount, BB_DIR_BIN, BB_SUID_DROP, umount))
* On one hand, in some weird situations you'd want umount
* to not do anything surprising, to behave as a usual fork+execed executable.
* OTOH, there can be situations where execing would not succeed, or even hang
* (say, if executable is on a filesystem which is in trouble and accesses to it
* block in kernel).
* In this case, you might be actually happy if your standalone bbox shell
* does not fork+exec, but only forks and calls umount_main() which it already has!
* Let's go with NOEXEC.
* bb_common_bufsiz1 usage here is safe wrt NOEXEC: not expecting it to be zeroed.
//kbuild:lib-$(CONFIG_UMOUNT) += umount.o
//usage:#define umount_trivial_usage
//usage:#define umount_full_usage "\n\n"
//usage: "Unmount file systems\n"
//usage: "\n -a Unmount all file systems" IF_FEATURE_MTAB_SUPPORT(" in /etc/mtab")
//usage: )
//usage: "\n -n Don't erase /etc/mtab entries"
//usage: )
//usage: "\n -r Try to remount devices as read-only if mount is busy"
//usage: "\n -l Lazy umount (detach filesystem)"
//usage: "\n -f Force umount (i.e., unreachable NFS server)"
//usage: "\n -d Free loop device if it has been used"
//usage: )
//usage: "\n -t FSTYPE[,...] Unmount only these filesystem type(s)"
//usage:#define umount_example_usage
//usage: "$ umount /dev/hdc1\n"
#include <mntent.h>
#include <sys/mount.h>
#ifndef MNT_DETACH
# define MNT_DETACH 0x00000002
#include "libbb.h"
#include "common_bufsiz.h"
#if defined(__dietlibc__)
// TODO: This does not belong here.
/* 16.12.2006, Sampo Kellomaki (
* dietlibc-0.30 does not have implementation of getmntent_r() */
static struct mntent *getmntent_r(FILE* stream, struct mntent* result,
char* buffer UNUSED_PARAM, int bufsize UNUSED_PARAM)
struct mntent* ment = getmntent(stream);
return memcpy(result, ment, sizeof(*ment));
/* ignored: -c -v -i */
#define OPTION_STRING "fldnrat:" "cvi"
#define OPT_FORCE (1 << 0) // Same as MNT_FORCE
#define OPT_LAZY (1 << 1) // Same as MNT_DETACH
#define OPT_FREELOOP (1 << 2)
#define OPT_NO_MTAB (1 << 3)
#define OPT_REMOUNT (1 << 4)
#define OPT_ALL (ENABLE_FEATURE_UMOUNT_ALL ? (1 << 5) : 0)
int umount_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int umount_main(int argc UNUSED_PARAM, char **argv)
int doForce;
struct mntent me;
FILE *fp;
char *fstype = NULL;
int status = EXIT_SUCCESS;
unsigned opt;
struct mtab_list {
char *dir;
char *device;
struct mtab_list *next;
} *mtl, *m;
opt = getopt32(argv, OPTION_STRING, &fstype);
//argc -= optind;
argv += optind;
// MNT_FORCE and MNT_DETACH (from linux/fs.h) must match
doForce = opt & (OPT_FORCE|OPT_LAZY);
/* Get a list of mount points from mtab. We read them all in now mostly
* for umount -a (so we don't have to worry about the list changing while
* we iterate over it, or about getting stuck in a loop on the same failing
* entry. Notice that this also naturally reverses the list so that -a
* umounts the most recent entries first. */
m = mtl = NULL;
// If we're umounting all, then m points to the start of the list and
// the argument list should be empty (which will match all).
fp = setmntent(bb_path_mtab_file, "r");
if (!fp) {
if (opt & OPT_ALL)
bb_error_msg_and_die("can't open '%s'", bb_path_mtab_file);
} else {
while (getmntent_r(fp, &me, bb_common_bufsiz1, COMMON_BUFSIZE)) {
/* Match fstype (fstype==NULL matches always) */
if (!fstype_matches(me.mnt_type, fstype))
m = xzalloc(sizeof(*m));
m->next = mtl;
m->device = xstrdup(me.mnt_fsname);
m->dir = xstrdup(me.mnt_dir);
mtl = m;
// If we're not umounting all, we need at least one argument.
// Note: "-t FSTYPE" does not imply -a.
if (!(opt & OPT_ALL)) {
if (!argv[0])
m = NULL;
// Loop through everything we're supposed to umount, and do so.
for (;;) {
int curstat;
char *zapit = *argv;
char *path;
// Do we already know what to umount this time through the loop?
if (m)
path = xstrdup(m->dir);
// For umount -a, end of mtab means time to exit.
else if (opt & OPT_ALL)
// Use command line argument (and look it up in mtab list)
else {
if (!zapit)
path = xmalloc_realpath(zapit);
if (path) {
for (m = mtl; m; m = m->next)
if (strcmp(path, m->dir) == 0 || strcmp(path, m->device) == 0)
// If we couldn't find this sucker in /etc/mtab, punt by passing our
// command line argument straight to the umount syscall. Otherwise,
// umount the directory even if we were given the block device.
if (m) zapit = m->dir;
// umount from util-linux 2.22.2 does not do this:
// umount -f uses umount2(MNT_FORCE) immediately,
// not trying umount() first.
// (Strangely, umount -fl ignores -f: it is equivalent to umount -l.
// We do pass both flags in this case)
#if 0
// Let's ask the thing nicely to unmount.
curstat = umount(zapit);
// Unmount with force and/or lazy flags, if necessary.
if (curstat && doForce)
curstat = umount2(zapit, doForce);
// If still can't umount, maybe remount read-only?
if (curstat) {
if ((opt & OPT_REMOUNT) && errno == EBUSY && m) {
// Note! Even if we succeed here, later we should not
// free loop device or erase mtab entry!
const char *msg = "%s busy - remounted read-only";
curstat = mount(m->device, zapit, NULL, MS_REMOUNT|MS_RDONLY, NULL);
if (curstat) {
msg = "can't remount %s read-only";
status = EXIT_FAILURE;
bb_error_msg(msg, m->device);
} else {
status = EXIT_FAILURE;
bb_perror_msg("can't unmount %s", zapit);
} else {
// De-allocate the loop device. This ioctl should be ignored on
// any non-loop block devices.
// Find next matching mtab entry for -a or umount /dev
// Note this means that "umount /dev/blah" will unmount all instances
// of /dev/blah, not just the most recent.
if (m) {
while ((m = m->next) != NULL)
// NB: if m is non-NULL, path is non-NULL as well
if ((opt & OPT_ALL) || strcmp(path, m->device) == 0)
// Free mtab list if necessary
while (mtl) {
m = mtl->next;
mtl = m;
return status;